National Instruments AT-MIO-16X - Manual (Page 189)

Chapter 5 Programming
AT-MIO-16X User Manual 5-20 © National Instruments Corporation
acquisition operation is terminated when Counter 4 and Counter 5 reach
zero.
Programming the Scan-Interval Counter
Counter 2 of the Am9513A Counter/Timer is used as the scan-interval
counter. Counter 2 can be programmed to generate a pulse once every
N counts. N is referred to as the scan interval, which is the time between
successive scan sequences programmed into the mux-channel gain
memory. N can be between 2 and 65,536. One count is equal to the
period of the timebase clock used by the counter. The following clocks
are available internal to the Am9513A: 5 MHz, 1 MHz, 100 kHz,
10 kHz, 1 kHz, and 100 Hz. In addition, the scan-interval timer can use
signals connected to any of the Am9513A SOURCE input pins.
To program the scan-interval counter, use the following programming
sequence. All writes are 16-bit operations. All values given are
hexadecimal.
1. Write FF02 to the Am9513A Command Register to select the
Counter 2 Mode Register.
2. Write the mode value to the Am9513A Data Register to store the
Counter 2 mode value. Use one of the following mode values:
8225 — Selects 5-MHz clock (Counter 2 Source signal)
8B25 — Selects 1-MHz clock
8C25 — Selects 100-kHz clock
8D25 — Selects 10-kHz clock
8E25 — Selects 1-kHz clock
8F25 — Selects 100-Hz clock
8525 — Selects signal at SOURCE5 input as clock
(counts the rising edge of the signal, 6 MHz maximum)
3. Write FF0A to the Am9513A Command Register to select the
Counter 2 Load Register.
4. Write 2 to the Am9513A Data Register to store the Counter 2 load
value.
5. Write FF42 to the Am9513A Command Register to load Counter 2.
6. Write FFF2 to the Am9513A Command Register to step Counter 2
down to 1.